The present invention relates generally to a circuit for interfacing voltage-mode logic by means of transmitting and receiving current signals, and more specifically to a fully-differential half-circulator for bi-directional small-signal signaling.
Multi-gigabit per second wireline (operating on physical wires) bi-directional communication is necessary for putting together the functional sub-units that make up high performance computers. These multi-gigabit per second wireline channels can connect multiple microprocessors, microprocessors and memory blocks, or any other high-performance logic units requiring high-speed data feeding.
Previous implementations of wireline signaling have tried to fight noise and jitter by using large-signals (signals having excursions in voltage comparable to the supply voltage values used) in the signaling scheme. Unfortunately, the use of large signals itself induces distortion into the signal, even though it was thought that the large amplitude of the signals would overcome the noise. It exposes the signals both to noise from the power supply lines, and to xe2x80x9cself-inflictedxe2x80x9d jitter. This is because large-signal signaling usually uses rail-to-rail voltage signals, thus making the amplitude of the signals defined by the value of the power supply. Therefore, fluctuations in power supply voltage will map directly into both fluctuations in the signal amplitude (noise) and fluctuation in the signal""s rising and falling edge rates (jitter).
Moreover, the use of large-signals signaling makes bi-directional signaling implementation unreliable at high data rates. This may occur because the receivers and transmitters are strongly upset by the signals themselves, compromising the receivers"" and transmitters"" ability to properly add and subtract signals, which are required operations for enabling bi-directional signaling.